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125 Years of Flight Testing

It is generally accepted that Otto Lilienthal (1848-1896) was the “father of gliding experiments.” We remember that during a period of about six years, he made over 2000 well-documented gliding flights, and that he died following a crash in 1896.

What is not as well known is that Lilienthal was a brilliant scientist and a revolutionary engineer. One hundred years after the first manned balloon flight, our understanding of mechanical flight had not advanced very much from the speculative art of Leonardo da Vinci.

It was Lilienthal’s life’s work to understand the mechanical principles that allowed birds to fly.

Through careful observation and experimentation, Lilienthal became convinced that:

A wing provides the lifting force that allows sustained flight, and it is not necessary for a wing to flap in order to do this.

The lifting force depends directly on the area of the wing, the shape of the wing, and the angle at which the wing meets the air.

The retarding force depends on the same quantities.

These truths were first published in his book, Der Vogelflug als Grundlage der Fliegekunst (Birdflight as a Basis for Aviation). This comprehensive treatise, published in 1889, can be considered to be the first book on the subject of aerodynamics, and it included a chapter in which the author made a clear case that the future of aviation belonged to heavier-than-air flight.

With the principles of mechanical flight thus established, the obvious next step would be to discover the design parameters for a machine that would be capable of carrying a man.

Without any help from wind tunnels or computers, Lilienthal began construction of the first aircraft to be used specifically for the purpose of investigating the relationship between lift and drag.

That aircraft first flew on a spring day in 1891, and the rest is history.